X-ray machines having a resolution that can be switched over on the camera side are preferably applied for photographing the heart or regions near the heart. As a rule, it is possible on the camera side to switch over between a pixel matrix with high resolution of, for example, 1024×1024 pixels, and a matrix with low resolution of, for example, 512×512 pixels, the reduction in resolution being performed by pixel binning. The advantage of this switchover resides, firstly, in that at a high image rate it is possible to reduce the detected data volume as a consequence of the reduction in resolution by comparison with the high-resolution matrix, a loss in resolution necessarily being accepted in the process. A further advantage is the lower noise by comparison with the high resolution, that is to say the noise component or the quantum noise is less for the low-resolution matrix.
However, even when a low resolution is set, the noise component still constitutes a problem that, in particular, raises difficulties for the physician observing the recorded image, since the image is noisy and unsteady.
DE 35 26 687 A1 relates to an X-ray diagnosis unit having an image intensifier with the aid of which an X-ray image generated by radiation with X-rays through an object to be examined is converted into a visible image. Also provided is a television camera that has a camera tube and serves for converting the photograph into a TV video signal.
So that an optimal image of a part of an object to be examined can be obtained, a control unit is provided via which the diameter of the photograph of the image intensifier, and the scanning area of the camera tube can be controlled in an interlocking fashion. The output signal or dynamic range and response time behave reciprocally relative to one another in a camera tube, and so it is the aim of D1 to render it possible with a single camera tube to obtain an image selectively with high resolution or a good response time.
The diameter of the photograph of the image intensifier is varied for this purpose. In accordance with the diameter of the photograph, the scanning area on the photocathode can be varied, and so it can, for example, be decreased given a reduced diameter such that the signal output current of the camera tube becomes smaller. The response time can be improved thereby. A reverse procedure is appropriate when a high resolution is desired.
Digital X-ray detector systems, in particular solid state detector systems, are described in “Fortschritte auf dem Gebiet der Röntgenstrahlen und der bildgebenden Verfahren” [“Advances in the field of X-rays and imaging methods”], volume 173, 2001, Offprint, Georg Thieme Verlag Stuttgart, pages 1137 to 1146, the contents of which are hereby incorporated herein by reference. However, with solid state detectors the sharpness of the image on the output screen is entirely unable to be varied by being switched over depending on the resolution set for the camera.
GB 2 186 149 A concerns the image differentiation by using charge-coupled components with masked pixels that are opaque to the radiation to which they are exposed. They further later serve as storage areas for the charge pattern of the unmasked pixels which are likewise provided.